June 1 - 3 , 1978 - University of Hawaii at Manoa

plant species diversity. The more diverse the vegetational com-
munity, the greater is the potential for species packing in the
consumer community and likewise in the entire trophic network.
In addition to trophic relationships, increased vegetational
diversity results in an increased spatial heterogeneity. There
is an increase in the complexity of the physical environment.
For example, the higher abundance of Psychotria sp. in lower
altitude plotsites means that there are differences in the trophic
niche, habitat changes in the litter layer, unique resiance
opportunities for day-inactive insect species, a new bark habitat
for the psocopteran and orthopteran families, etc. Ip short, the
more complex the physical environment becomes, the more complex
the plant and animal communities supported, and the higher the
Species diversity. MacArthur (1965) suggested that betweenr
habitat diversity is a major scheme in determining tropical
species packing. For example, MacArthur and MacArthur (1961)
determined that the extent of foliage stratificatio~ in a forest
community was more important than the species diversity of the
vegetational community alone in affecting the faunal diversity.
In the Manuka study, foliage stratification increased with lower
altitude, as conditions improved for tree species. A t the 1150 m
plotsites, the canopy of Metrosideros was non-interlocking and
rose to about 6 m. Forest conditions developed by 875 m, however,
with densely interlocking canopies of Metrosideros and
Psychotria, reaching crowns at 25 m. The substantially tall
canopy created adequate room for a well-developed middle-story of
Cibotium tree ferns, M rsine lessertiana, and Vaccinium calycinum,
and an understory ---T o ferns and small vascular plants. In
the585 m plotsites, species diversity was even higher, and the
complexity~of foliage stratification was very well developed. It
is not surprising that the increase in species diversity and
foliage stratification downslope in the study area is paralleled
by a correspondant
community.
increase in the diversity of the insect
- . -
Combination of factors
All of the factors discussed this far cannot be realis-
tically considered independently. The combination of environ-
mental aspects and biotic factors is a dynamic process, the
synthesis of which is the final characteristics of insect distri-
bution we have observed. For example, moisture characteristics
probably determined the basic vegetational diversity at 875 m;
however, the presence of vegetation can create microclimates in
which moisture and temperature conditions are quite different
from adjacent, barren areas at the same altitude. As a result,
the increase in the complexity of the environment created by
microclimates would allow for a higher potential in species
diversity. What will be discussed next is an example of the
resultant effect of a combination of environmental and biotic
factors: the "hump" phenomenon at 1440 m.